Researchers at the University of Waterloo have now shown that the lightweight superconductor MgB2 (magnesium diboride)—the average mass/atom of which is comparable with carbon—as a metallic sulfur host fulfills both electron conduction and polysulfide immobilization properties.

In a paper in the journal Joule the teams reports that, by using first-principles calculations, they found that borides are unique in that both B- and Mg-terminated surfaces bond exclusively with the Sx2− anions (not Li+), and hence enhance electron transfer to the active Sx2− ions.

The surface-mediated polysulfide redox behavior results in a much higher exchange current in comparison with MgO and carbon. By sandwiching MgB2 nanoparticles between graphene nanosheets to form a high-surface-area composite structure, they demonstrated sulfur cathodes that achieve stable cycling at a high sulfur loading of 9.3 mg cm−2.

They conclude that this new avenue toward Li-S cathodes, when coupled with a protected lithium metal anode, may lead to practical implementation of batteries that are lighter, yet robust.